An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

Math.: 1) Of or pertaining to a linear transformation from a vector space to itself that is not one-to-one.
2) Of or pertaining to a matrix having a determinant equal to zero.

M.E., from O.Fr. singuler "single, separate," from L. singularis "single, solitary," from singulus "one, individual, separate," from sim- (stem of simplus) + diminutive suffix.

Takin, from tak "single, alone," related to tâq "odd, single," tâ, tâh "piece, part; fold, plait, ply;" Mid.Pers. tak "single," tâg, tâk, tâi "unit, piece, after numerals" + -in adj. suffix.

In models of star formation, an isothermal sphere in which the density distribution in the static or nearly static outer envelope obeys an r^-2 power law. In the limit of infinite central concentration, the unstable equilibrium approaches the singular isothermal sphere which has the density and mass distributions ρ(r) = (a²/2πG)r^-2 and M(r) = (2a²/G)r, where a is the isothermal → sound speed inside the cloud, G is the → gravitational constant, and r the distance from the center (F. H. Shu, 1977, ApJ 214, 488).

→ singular; → isothermal; → sphere.

A → square matrix that does not have a → matrix inverse.

→ singular; → matrix.

The point M₀(x₀,y₀) of the curve F(x,y) = 0, where at least one of the → partial derivatives ∂F/∂x and ∂F/∂y vanishes. See also → ordinary point.

→ singular; → point.

Of partial differential equations, the solution which cannot be obtained from the general solution by particular choice of arbitrary functions. → general solution; → particular solution.

→ singular; → solution.

1) Math.: A point at which a given mathematical object is not defined.
2) Physics: A point in → space-time in which gravitational force causes space-time to have infinite curvature; matter is crushed to infinite density and zero volume. This happens at the center of a → black hole where space and time cease to exist as we know them, and the known laws of physics break down. See also → Schwarzschild singularity; → initial singularity.

→ singular + → -ity.

1) A region within a system where mass or energy is given up, in contrast to a → source, where mass or energy is released.
2) In hydrodynamics simulation codes of gaseous collapse and → accretion, such as → smoothed particle hydrodynamics (SPH), a region of the flow that accretes incoming material but that does not allow it to leave. In in theses simulations an enormous dynamic range is usually encountered, which makes the full problem computationally infeasible. Indeed dynamic range requires enough resolution elements in both space and time to resolve the largest and smallest scales present in the problem. Sinks provide a way of concentrating resolution in regions of interest and evolving different regions with different time-steps. These entities can have stellar scale masses. See also → sink particle.

M.E. sinken, O.E. sincan, from verb; cf. O.S. sinkan, O.N. sökkva, M.Du. sinken, Du. zinken, O.H.G. sinkan, Ger. sinken, Goth. sigqan "to sink."

Câhak, from câh "a well" (Mid.Pers. câh "a well;" Av. cāt- "a well," from kan- "to dig," uskən- "to dig out;" O.Pers. kan- "to dig;" Mod.Pers. kandan "to dig;" cf. Skt. khan- "to dig," khanati "he digs," kha- "cavity, hollow, cave, aperture") + -ak diminutive suffix.

In hydrodynamics codes, a way of treating a collapsing or accreting region, such as a star, as a simple → point mass. Indeed, in many situations, the scale of interest is much larger than the scale of the → accreting object itself and it would be impossible to perform the calculation otherwise. → Sinks are generally modeled as → Lagrangian particles (see, e.g., Bates et al. 1995, MNRAS 277, 362; Krumholz et al. 2004, ApJ 611, 399; Federrath et al. 2010, ApJ 713, 269).

→ sink; → particle.

The outermost of Jupiter's known confirmed satellites, also known as Jupiter IX, discovered by Seth B. Nicholson (1891-1963) in 1914. With a visual magnitude of 18.3, it has a diameter of 28 km and orbits Jupiter at a mean distance of 23,848,000 km every 753 days.

In Gk. mythology a Naias Nymphe who was abducted by Zeus to a Black Sea coast where the city of Sinope was named for her. According to most sources, she tricked Zeus into swearing an oath promising her her virginity.

Having the characteristics of a sine function; same as → sine wave.

From sinus, → sine, + → -al.

1) To drink (a liquid) a little at a time; take small tastes of.
2) An instance of sipping; a small taste of a liquid; a small quantity taken by sipping (Dictionary.com).

M.E. sippen (v.), akin to Low German sippen "to sip."

Cašel, from Pashto cašəl "to drink," caceq "to drip;" related to cašidan "to taste," → taste.

A ∩-shaped tube with unequal arms that is used to move a liquid from one level to a lower level via a third level higher than either. Once the short arm is filled, for example, by suction, the liquid flows down in the long arm under the action of gravity due to mass excess in it.

From Fr. siphon, from L. sipho (genitive siphonis), from Gk. siphon "pipe, tube," of unknown origin.

The white star in the constellation → Canis Major that is the brightest star of the sky (V = -1.46). Its other designations include HD 48915, HR 2491, and BD-16°1591. Its particular brightness is mostly due to its proximity to the Earth, being a mere 8.6 → light-years away, the fifth closest star system. Sirius is a → dwarf star of → spectral type A0 or A1 V with an → effective temperature of 9,880 K, a mass of 2.063 ± 0.023 Msun (Bond et al., 2017, ApJ 840, 70), and a → luminosity of 26 Lsun. Sirius has a radius of 1.75 solar and a minimum equatorial rotation speed of 16 km s^-1. Its → rotation period is less than 5.5 days. This star is a → visual binary (separation 4.6 arcsec, period 50 years), the companion → Sirius B being the first → white dwarf to be discovered. Sirius is a → metal-rich star, its iron content triple that of the Sun, most likely from some sort of → element diffusion.

From L. Sirius, from Gk. Seirios, literally "scorching," because of its brightness.

Tištar, from Mid.Pers. Tištar, from Av. Tištrya- "(name of the deified star) Sirius," literally "the one who belongs to the three stars," in reference to the three stars of → Orion's Belt; ultimately from PIE *tri-str-o-m- "group of three stars," then *tri-str-iia- and by dissimulation Indo-Iranian *ti-str-iia-, Av. *Tištriia- and Vedic Skt. Tisyà (A. Panaino, in Iranica, under Tištrya).

Same as → companion of Sirius.

→ Sirius; B, letter of alphabet by convention.

Same as → Alpheratz.

Sirah, contraction of Ar. As-Surrat al-Faras (السره‌الفرس) "The Horse's Navel," from surrat (سره) "navel" + faras (فرس) "horse." The name refers to the location of the star in the figure of → Pegasus. However, the star is now considered to belong to the constellation → Andromeda.

Ra's-ol-Mosalsalé, from Ar. Ar-Ra's al-Mar'ah al-Musalsalah "The head of the chained woman," from Ra's "head" + Mar'ah "woman" + Musalsalah "chained".

In a → superheterodyne receiver, a → mixer which consists of a sandwich structure of two superconducting leads separated by a thin isolator. SIS mixers give a good noise performance especially for → millimeter wavelengths.

SIS, acronym for Superconductor-Insulator-Superconductor; → mixer.

A female person having the same parents as another person.

M.E. suster, sister, from O.E. sweostor, swuster or Old Norse systir, in either case ultimately from PIE *swesor; cf. Skt. svásar-, Av. x^vaηnhar-, Pers. xâhar, xwâhar, as below, Gk. eor, L. soror (Fr. sœur), O.C.S., Rus. sestra, O.Ir. siur, Sw. syster, Dan. soster, O.Sax. swestar, M.Du. suster, Du. zuster, O.H.G. swester, Ger. Schwester.

Xâhar, xwâhar, from Mid.Pers. xwah(ar) "sister;" Av. x^vaηnhar- "sister;" cf. Khotanese hvar- "sister;" cognate with E. sister, as above.

1) To rest with the body supported by the buttocks or thighs; be seated.
2) To be located or situated.

Nešastan "to sit down; to settle down; to sink;" Mid.Pers. nišastan "to sit;" O.Pers. nišādayam [1 sg.impf.caus.act.] "to sit down, to establish," hadiš- "abode;" Av. nišasiiā [1 sg.subj.acr.] "I shall sit down," from nihad- "to sit down," from → ni- "down; into" + had- "to sit;" PIE base *sed- "to sit;" cf. Skt. sad- "to sit," sidati "sits;" Gk. hezomai "to sit," hedra "seat, chair;" L. sedere "to sit;" O.Ir. suide "seat, sitting;" Welsh sedd "seat;" Lith. sedmi "to sit;" Rus. sad "garden;" Goth. sitan, Ger. sitzen; E. sit. See also: → reside, → settle.

The position or location of a building, observatory, etc. especially as to its environment. → astronomical site.

M.E., from L situs "position, arrangement, site," from sinere "to let, leave alone, permit," cognate with Av. šiti- "place, abode, residence," as below.

Sit, from Av. šiti- "place, abode, residence," šitāy- "habitation, dwelling," from ši- "to live;" cognate with Skt. ksay- "to live, to stay," kséti "he dwells;" Gk. ktizein "to inhabit, build;" L. situs "position, site; situated."

The process of choosing a site for an astronomical observatory based on meteorology, seeing conditions, and access to the site.

→ site; → selection.